<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .windmill1 {
            width: 400px;
            height: 400px;
            border: 1px solid #000;
        }
        .item {
            width: 0;
            height: 0;
            float: left;
            border: solid 100px;
        }
        .item1 {
            border-color: transparent transparent red transparent;
        }
        .item2 {
            border-color: transparent transparent transparent red;
        }
        .item3 {
            border-color: transparent red transparent  transparent;
        }
        .item4 {
            border-color: red transparent transparent transparent;
        }

        .trapezoid {
            width: 100px;
            height: 0;
            border-style: solid;
            border-width: 100px 0 100px 100px;
            border-color: transparent transparent blue transparent;
        }
    </style>
</head>
<body>
    <div class="windmill1">
        <div class="item item1"></div>
        <div class="item item2"></div>
        <div class="item item3"></div>
        <div class="item item4"></div>
    </div>

    <div class="trapezoid"></div>
</body>
</html>